1. Field of the Invention
This invention concerns a porous ceramic structure having a good wettability with molten metal and thus suitable for use as a filter for molten metal.
2. Description of the Prior Art
Demands for aluminum products such as aluminum cans for drinks and aluminum foils for packaging use, as well as copper wires for use in electrical conduction wires have been increased more and more in recent years. Since pin holes, wire disconnections or like other defects are resulted in such aluminum or copper products if solid impurities are present in the ingots for producing them, various attempts have been made for obtaining the purified ingots having no solid impurities.
Such the ingots are produced from the purified molten fresh metal obtained by filtering the molten fresh metal to remove solid impurities therefrom. Conventionally, as the filter for molten metal, alumina balls of several millimeter diameter or sinters of alumina particles have hitherto be used for filtering out the impurities by passing the molten metal therethrough.
In order to further improve the filter for molten metal, the present applicant has already proposed porous ceramic filters as described in Japanese patent publications Nos. 35047/1982, 35048/1982, 35049/1982 and 13887/1984, which have already been put to practical use generally in the field of metal material production.
Although the above proposed ceramic filters have been appreciated as filters of high industrial value and the demand therefor has increased, the filters made from ceramic are generally poor in wettability between the ceramics and the molten metal and, accordingly, they involve the following problems, for which effective solutions are required:
(1) They require a long period of time from the introduction of a molten metal at the inlet of the filter to the start of the actual filtration of the molten metal, as well as a large initial head.
(2) They cause a localized flow of the molten metal inside of the filter to hinder the effective utilization for the entire region of the filter, as well as give a high flow resistance to the molten metals to reduce the filtering rate and the processing amount of the molten metal, resulting in reduction in the durability.